fix(web): honor selected DWG/DXF version when saving

The web save path discarded the chosen format version (`let _ = version`)
and `save_to_bytes` never applied it, so every browser download was
written at the document's default version (AC1032 / DWG 2018) regardless
of the format picked in the Save dialog. (#122)

Thread `version` into `save_to_bytes` and set `doc.version` there, the
byte-buffer counterpart to `save_as_version`. Saving as DWG 2013 now
writes an AC1027 file.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/update.rs

@@ -976,8 +976,7 @@ impl OpenCADStudio {
                 }
                 #[cfg(target_arch = "wasm32")]
                 {
-                    let _ = version;
-                    match crate::io::save_to_bytes(&self.tabs[i].scene.document, ext) {
+                    match crate::io::save_to_bytes(&self.tabs[i].scene.document, ext, version) {
                         Ok(bytes) => {
                             crate::sys::download_bytes(&filename, &bytes);
                             self.tabs[i].dirty = false;

src/io/mod.rs

@@ -357,10 +357,17 @@ pub fn save(doc: &CadDocument, path: &Path) -> Result<(), String> {
 }
 
 /// Serialize a document to an in-memory byte buffer, format chosen by `ext`
-/// (`dxf` → DXF, anything else → DWG). Used by the web build, which hands the
-/// bytes to a browser download instead of writing a path.
-pub fn save_to_bytes(doc: &CadDocument, ext: &str) -> Result<Vec<u8>, String> {
+/// (`dxf` → DXF, anything else → DWG) at the given DXF version (overriding
+/// `doc.version`). Used by the web build, which hands the bytes to a browser
+/// download instead of writing a path — the byte-buffer counterpart to
+/// [`save_as_version`].
+pub fn save_to_bytes(
+    doc: &CadDocument,
+    ext: &str,
+    version: acadrust::DxfVersion,
+) -> Result<Vec<u8>, String> {
     let mut doc = doc.clone();
+    doc.version = version;
     sync_current_styles_on_save(&mut doc);
     match ext.to_lowercase().as_str() {
         "dxf" => DxfWriter::new(&doc).write_to_vec().map_err(|e| e.to_string()),